Mary

Mary Lake (DOW# 77-0019-00; Lake Class 34) is a 129-acre lake located near Upsala, Minnesota. A Minnesota Department of Natural Resources (MNDNR) owned concrete boat ramp is located on the northeast shore. Mary Lake has 4.52 miles of shoreline and a maximum depth of 58 feet. The lake is primarily managed for Bluegill and Northern Pike and secondarily for Walleye, Black Crappie, and Largemouth Bass. The lake was initially surveyed in 1969, and 16 fish sampling surveys or investigations have occurred since then. A standard survey using six gill nets and nine standard trap nets was completed on Mary Lake during the week of June 30,2025. Gill netting captured a total of six species; the most abundant species being captured were Black Bullheads at 485 and Northern Pike at 150. Northern Pike ranged in size from 15.6 to 33.8 inches. Other species included Black Crappies, Walleye, White Sucker, and Yellow Bullhead. The average size for Walleye captured was 19.9 inches. Trap nets caught a total of fourteen species, the most abundant being Black Bullheads. Bluegills were the second highest species captured at 28.11 fish per trap net which is high for this type of lake, this is very encouraging after the 2023 winterkill. A 5 fish bag limit for sunfish was implemented on Mary Lake in 2021 as part of the statewide Quality Sunfish Initiative. Other species that were captured were Northern Pike, Hybrid Sunfish, and Black Crappie. The Northern Pike population continues to be mostly in the range of 18 to 21 inches with a few above 30 inches. Black Crappies averaged 5.5 to 6 inches.

A standard survey using six gill nets and nine standard trap nets was completed on Mary Lake during the week of July 3, 2023. Two targeted trap nets were set in mid-May to assess impacts from a suspected winterkill. Catch results confirmed the occurrence of a partial but significant winterkill. Species captured included bullheads (mostly Black), Black Crappie (many), Northern Pike, Yellow Perch, and Bowfin. Large numbers of dead sunfish, carp, bass, Walleye, and crappie were observed. The evidence suggests that the fish kill likely eliminated (Walleye) and severely depressed bass and sunfish populations. Electrofishing earlier in the spring indicated the presence of live Largemouth Bass and Bluegill though in small numbers. Walleye fingerlings were stocked in the fall of 2023. Conditions may be ideal for Walleye fingerling survival due to reduced pike abundance and competition from other fish species. Mary Lake is primarily managed for Bluegill and Northern Pike and secondarily for Walleye, Black Crappie and Largemouth Bass. Gill netting captured a total of six species with Black Bullheads and Northern Pike the most common species captured. Other species captured included Black Crappie, Brown Bullhead, Yellow Bullhead, and Yellow Perch. Trap nets caught a total of eight species, the most common of which were Bluegills. Although numbers were lower they were still within the range we'd expect to see in a lake like Mary. Mary Lake was selected for inclusion in the statewide Quality Sunfish Initiative (QSI) which attempts to protect and/or enhance the quality of sunfish fisheries. While uncommon for Mary Lake, the recent winterkill unfortunately set back progress at achieving a better Bluegill fishery. Growth rates are very good though, and we expect the fishery to rebound quickly. Species other than Bluegill that were caught in trap nets included Bowfin, Green Sunfish, Hybrid sunfish, and Pumpkinseed. Mary Lake's fishery prior to the 2023 winterkill can be characterized as supporting an abundance of small pike and a low-density Walleye population as evidenced by the 2017 survey. Pike over 30 inches continue to reside in Mary Lake. Black Crappie and Bluegill were abundant, with Bluegill showing high rates of growth but only small to average size-quality. Crappie growth rates were poor presumably due to a high density population. Hopefully crappie growth rates improve with the lowered abundance resulting from the winterkill. The Largemouth Bass population was considered good with multiple year classes present.

Spring Trap netting was performed May 19-21 to provide pre-regulation data on the Bluegill size structure. A 5 fish bag limit on sunfish was implemented on March 1, 2021, as Mary Lake was selected for participation in the statewide Quality Sunfish Initiative. Information collected during this survey is considered pre-regulation data due to the short time period since the inception of the reduced bag limit. Spring trap netting is the preferred method for evaluating panfish populations and has been conducted on the lake four previous times since 2000. Several future evaluations relating to the 5 sunfish bag limit are planned over the 10 year evaluation period and will incorporate spring trap netting to provide proper comparisons. Spring trap netting in 2021 captured 493 Bluegill. Bluegill in 2021 ranged from 3.4 - 8.35 inches and mean length was 6.03 inches. Fish over 7 inches comprised 39% of the catch and fish greater than 8 inches made up just 0.2% of the sample. Fish 8 inches or longer have never made up more than 3% of spring samples and Bluegill 9 inches or greater have not been observed in any spring trap net efforts. Bluegill grow well in Mary Lake reaching 7.5 inches by Age 5 but few fish appear to exceed six years of age. The objective of the reduced sunfish bag limit is to curtail harvest of sunfish so that more reach greater ages and larger sizes. Bluegill size structure goals developed for the Quality Sunfish Initiative aim for at least 35% of the sample to exceed 7 inches, 10% to exceed 8 inches and 2% over 9 inches. Whether voluntary or required due to the reduced bag limit, release of larger sunfish, especially fish over 8 inches will be important if the lake is to realize its potential in reaching management goals. Additional criteria that may be used to measure success of the reduced sunfish bag limit include: mean size, catch rate of fish over 8 inches, and mean length of top 10% of fish. When combining the five pre-regulation spring trap net surveys mean size is 5.85 inches, mean catch rate of fish over 8 inches is 1/net, and mean length of the top 10% is 7.60 inches. Spring trap nets produced a large catch of Black Crappie totaling 803 fish. Small crappie dominated the sample, as a strong year class was generated in 2015. The 2021 Black Crappie ranged from 4.8 to 10.8 inches in length and mean length was 6.99 inches. Fish 10 inches or longer have never comprised a major portion of the spring catches. Only 1 crappie over 10 inches was measured in 2021 and fish over 11 inches have never been observed in spring trap nets. Aging in 2021 showed the 2015 year class continued to comprise a significant proportion of the population. The 2015 year class exhibited poor growth attaining a mean length of 7.22 inches at Age 6. The currently poor growth is a new factor as all previous information suggested normal growth rates in the past. The slow growth is likely due to the exceptionally high abundance. Anglers are encouraged to harvest crappie from Mary Lake to reduce the population and improve growth. The crappie bag limit remains at 10 fish. Recruitment has been sporadic recently as Ages 2 and 6 made up the entire catch with the exception of a single Age 10 individual. Four Northern Pike were caught, three of which exceeded 29 inches and the largest measuring 33.2 inches. Some Yellow Perch in excess of 8 inches were also observed and may be of interest to anglers.

Based on Minnesota DNR survey data, anglers target Largemouth Bass, Bluegill, Hybrid Sunfish, Green Sunfish, and Black Crappie in Mary. See the full species list above for catch rates, size structure, and quality scores.

Minnesota DNR records list public access for Mary. Check the DNR LakeFinder page for the launch type and directions before you go.

Mary has a maximum depth of 58 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in Mary is from 2025.

Yes — Mary has confirmed Eurasian watermilfoil. Clean, drain, and dry your equipment to avoid spreading invasives to other waters.